Page 194 - Materials Chemistry, Second Edition

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Sustainability of Municipal Solid Waste Management
Exhaust 173
Water gases
Softener
Boiler Cooling
Fuel
tower
Warm Cold
Steam
water water
Bone Crushed Bone
waste Bone bones Steam + Fat Centrifugal Bones
crusher cooker separator Cooler
Fat Bones

Packaging Calcium
Calcium powder Hummer mill
unit powder
FIGURE 5.18 Bone recycling process

• Fine grinding: The cooled bones are transferred from the cooler to the
hummer mill using an auger to obtain finer grains of calcium powder.
• Cyclone separator: A two-stage cyclone separator is used to separate
the calcium powder before backing.
• Packing: At this stage the fine grains are weighed, packed, and are
ready for marketing.

5.6 Recycling of Glass

Glass is a combination of sand and other minerals that are melted together
at very high temperatures to form a material that is ideal for a wide range of
uses from packaging and construction to fiber optics. As early as 4000 BC glass
was used in the Middle East as a glaze to decorate beads. By 1550 BC, colored
glass vessels were widespread and used for cooking and drinking. Until the
late 18th century and early 19th century glass was very expensive and was
used for limited applications, such as stained glass windows for churches.
Large-scale glass manufacture began with the industrial revolution and the
mass production of glass containers began at the onset of the 20th century.
Today the glass-making process can be used to make many different types
of glass in infinitely varied colors formed into a wide range of products. Glass,
chemically, is actually more like a liquid, but at room temperature it is so
viscous or “sticky” it looks and feels like a solid. At higher temperatures glass
gradually becomes softer and more like a liquid. It is this latter property that
allows glass to be poured, blown, pressed, and molded into a variety of shapes.
Nowadays glass is much less expensive and is taken for granted as a pack-
aging material in addition to its use in windows, doors, and other applications.